Today steam is used in many different processes. The steam is produced in different types of steam generators, which have mutually different properties.
Some types of steam generators thus have continuous, whereas other have intermittent steam capacity. Heating can be carried out with electric heating or by combustion of oil or by aid of other energy sources. Due to the specific applications for which the steam generator is intended, and also in view of the expected life span, the size thereof furthermore can vary and also the material from which it is manufactured.
At one type of such steam generators primarily intended for autoclaves is used an aluminium body with an internal cavity. The aluminium body is heated, whereupon water is sprayed into the cavity in the body, and is vaporized at contact with the body.
A drawback of this solution is that the steam pressure is controlled in dependence of the water volume sprayed in. If too much water is sprayed into the cavity, the pressure will become too high. The temperature of the body can not be lowered too much, as all the water in such case can not be vaporized immediately, but water will remain in the cavity and after boil. In order to prevent this the body must be made heavy. Simultaneously this solution requires that the steam generator is equipped with spraying nozzle and has a connection to water of high pressure.
At another solution is used a water container, which is heated to high temperature, whereby the water is used for storing the energy. A water container for such a steam generator must be built for high pressure, as water of higher temperature gives higher pressure. Furthermore it is a drawback, that the steam delivered has high pressure and high temperature, which can involve control technical problems at the place of use.
At still another earlier solution direct electric steam generation is brought about by means of electrodes, whereby the steam generation can be controlled either via the water level in the steam generator or via the electric current applied.
A drawback with this solution is that energy storing is effected only in the form of steam, and it furthermore is not possible to use de-ionizised water, as this has a too low conductivity.
SE-C-161.717 describes a steam generator having a heating element with an internal cavity to which water from above is supplied in a coil positioned in the cavity and equipped with an internal heating coil, and with a restricted water outlet situated a short distance above the bottom of the vessel, and an outlet for overheated steam provided at the upper part. Due to this design of the vessel the flow control of water will be made difficult, at the same time as the steam generator requires a rather large quantity of supplied heat due to the necessity to heat water, cause it to evaporize and furthermore to overheat the steam produced.